(57) A process for the manufacture of multi-layered thermoplastic containers (13) which
have integral multilayer bottom (15) and side walls (14), the top of the side walls
being circumferentially provided with a single layer flange (18) adapted to be interfolded
with metal closures (19) for sealing.
In order to simplify the manufacture of the containers and thereby to reduce the cost
of the containers, they are made by preparing a multilayer billet (10) having a first
and second thermoplastic layer (12, 11). the layers being so adapted that when the
thermoplastic material of the layers is heated to the heat softened state and a compressive
force is imposed thereon, the first layer (12) is extruded at a faster flow rate than
the second layer (11);
heating the billet (10) to place the layers (12.11) in the heat softened state;
compressing the billet (10) to cause the extrusion of the heat softened layers (12,
11) into a mold cavity whereby the fastest moving layer (12) forms the flange (18)
and exterior surface portions (16) of the container (13) and the slower of the layers
(11) forms the interior surface portion (17) of the container (13).
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